This invention relates in general to hub assemblies and more particularly to a hub assembly which accommodates rotation about an axis with a change in angular velocity.
Some vehicles rely on electric motors to power their wheels, and these motors are typically located at the wheels themselves—one for each driven wheel. But the wheels often require torques of large magnitude to rotate them. To reduce the torque demands, the wheel assemblies often include speed-reducing devices, and they may take the form of planetary gear drives.
Such wheel assemblies are not altogether satisfactory. First they are complex, with some of the complexity residing in the co-existence of gear drives and antifriction bearings which transfer the weight of the vehicle chassis to the wheels. In this regard, the planetary gears do not have the capacity to transfer radial loads themselves. Moreover, gear drives generate noise and consume energy inasmuch as the teeth of the gears, where they mesh, slide over each other. Also gear drives require oil lubrication, which is difficult to provide at the remote locations of the wheels.
In my prior U.S. Pat. No. 6,095,940, which is incorporated herein by reference, I disclosed a traction drive transmission. That traction drive included a two piece shaft surrounded by a two piece ring segment, each of which have a tapered raceway. A roller is positioned between the shafts and the ring segments and rotates about an axle which is supported by a roller carrier. The rollers frictionally engage the tapered raceways of the ring segment and shaft segments. Thus, when the shaft is rotated, rotational energy is transmitted to the rollers and hence to the ring segments and roller carrier. The traction drive described in the U.S. Pat. No. 6,095,940 patent transmits outwardly directed forces adequately to rotate the wheel. However, the construction of this drive does not enable the assembly to bear external loads from wheels. When the ring is mounted to a wheel, loads from the wheels are transmitted from the wheel to the ring and to the roller and then to the roller axle. The roller axle can move radially relative to the shaft. Thus, when the wheel exerts a radially inwardly directed force to the roller axle, the roller axle will move radially inwardly, allowing the roller to more forcefully engage the shaft. Hence, the radially inwardly directed wheel forces are transmitted to the shaft.